Plug in the mobile and get to relax (7,2)
I believe the answer is:
lighten up
'to relax' is the definition.
(to lighten up is to relax or be less serious)
'plug in the mobile' is the wordplay.
'mobile' indicates an anagram (mobile can mean moving).
'plug'+'in'+'the'='pluginthe'
'pluginthe' anagrammed gives 'LIGHTEN UP'.
'and get' is the link.
(Other definitions for lighten up that I've seen before include "Plug in the fire" , "Unwind" , "Relax!" , "Chill" .)